Serotonin is released by mast cells, basophils,
and platelets, and acts as a mediator of
inflammation and allergic reactions
(see allergy). It plays an important role
in blood clotting, stimulating a
strong heart beat, initiating sleep, fighting
depression (prescription drugs that treat depression raise the brain's levels
of serotonin), and causing migraineheadaches
in susceptible individuals (because of its ability to constrict blood vessels
or cause them to spasm). In the digestive tract, serotonin inhibits gastric
secretion and stimulates smooth muscle
in the intestine wall.

Serotonin agonists

Serotonin agonists are a group of drugs, also known as 5HT1 agonists,
used to treat acute attacks of migraine (caused by dilation of blood vessels
in the brain). They act on the same receptors in the brain as serotonin,
returning the dilated vessels to their normal size and so relieving symptoms.
Common serotonin agonists include naratriptan and sumatriptan. These drugs
can cause chest pain, particularly in people with heart disease, and should
be used with caution in those at risk of coronary
artery disease. Other side effects include flushing, tingling, and nausea.

Serotonin antagonists

Serotonin antagonists are a group of
drugs, also known as 5HT3 antagonists, used to treat nausea and
vomiting caused by radiotherapy and anticancer
drugs or following general anesthesia. Symptoms occur when serotonin stimulates
the vomiting center in the brain; the drugs inhibit the action of serotonin.
Common examples of serotonin antagonists are granisetron and ondansetron.